Second Harmonic Generating Research Articles

Biodegradable Harmonophores for Targeted High-Resolution In Vivo Tumor Imaging.

Optical imaging probes have played a major role in detecting and monitoring a variety of diseases. In particular, nonlinear optical imaging probes, such as second harmonic generating (SHG) nanoprobes, hold great promise as clinical contrast agents, as they can be imaged with little background signal and unmatched long-term photostability. As their chemical composition often includes transition metals, the use of inorganic SHG nanoprobes can raise long-term health concerns. Ideally, contrast agents for biomedical applications should be degraded in vivo without any long-term toxicological consequences to the organism. Here, we developed biodegradable harmonophores (bioharmonophores) that consist of polymer-encapsulated, self-assembling peptides that generate a strong SHG signal. When functionalized with tumor cell surface markers, these reporters can target single cancer cells with high detection sensitivity in zebrafish embryos in vivo. Thus, bioharmonophores will enable an innovative approach to cancer treatment using targeted high-resolution optical imaging for diagnostics and therapy.

Preparation and characterization of single crystals of tetrakis(4-(5,5-dimethyl-2-phenyl-1,3-dioxan-2-yl)phenyl)germane

A novel tetrakis(4-(5,5-dimethyl-2-phenyl-1,3-dioxan-2- yl)phenyl)germane (2) was synthesized by the reaction of germanium(IV) tetrachloride with 4-(5,5-dimethyl-2-phenyl-1,3-dioxan-2-yl)phenyllithium. Colorless plate-shaped single crystals obtained from recrystallization in ether were characterized by the single-crystal X-ray diffraction. The organogermanium compound was crystallized in a noncentrosymmetric nonpolar tetragonal space group, I-4, and classified as a porous molecular material owing to the presence of two types of distinct channels as a result of intermolecular hydrogen bonding. Compound 2 exhibits a differential gas adsorption property. The powder second-harmonic generating (SHG) measurements indicate that compound 2 shows a SHG efficiency 10 times greater than those of α-SiO2 and type-1 nonphase-matchable.

Effective Labeling of Primary Somatic Stem Cells with BaTiO3 Nanocrystals for Second Harmonic Generation Imaging.

While nanoparticles are an increasingly popular choice for labeling and tracking stem cells in biomedical applications such as cell therapy, their intracellular fate and subsequent effect on stem cell differentiation remain elusive. To establish an effective stem cell labeling strategy, the intracellular nanocrystal concentration should be minimized to avoid adverse effects, without compromising the intensity and persistence of the signal necessary for long-term tracking. Here, the use of second-harmonic generating barium titanate nanocrystals is reported, whose achievable brightness allows for high contrast stem cell labeling with at least one order of magnitude lower intracellular nanocrystals than previously reported. Their long-term photostability enables to investigate quantitatively at the single cell level their cellular fate in hematopoietic stem cells (HSCs) using both multiphoton and electron microscopy. It is found that the concentration of nanocrystals in proliferative multipotent progenitors is over 2.5-fold greater compared to quiescent stem cells; this difference vanishes when HSCs enter a nonquiescent, proliferative state, while their potency remains unaffected. Understanding the nanoparticle stem cell interaction allows to establish an effective and safe nanoparticle labeling strategy into somatic stem cells that can critically contribute to an understanding of their in vivo therapeutic potential.

M4Mg4(P2O7)3 (M = K, Rb): Structural Engineering of Pyrophosphates for Nonlinear Optical Applications

On the basis of their short ultraviolet (UV) absorption edges, phosphates are ideal candidates for deep-UV nonlinear optical (NLO) applications. However, their often-weak second-harmonic generating (SHG) responses reduce their NLO applications. It has been demonstrated that the SHG response in polyphosphates or orthophosphates could be enhanced by highly polymerized P–O groups or aligned nonbonding O-2p orbitals of isolated PO4 units. Herein, we report on the design and synthesis of two pyrophosphates, K4Mg4(P2O7)3 and Rb4Mg4(P2O7)3, with potential NLO applications. Both materials exhibit relatively large SHG responses with 1064 nm radiation, 1.3× and 1.4× KH2PO4 (KDP) for K4Mg4(P2O7)3 and Rb4Mg4(P2O7)3, respectively. In addition, absorption edges below 200 nm were observed for both materials. For K4Mg4(P2O7)3, single crystal vacuum-UV transmission measurements revealed an absorption edge of 170 nm. First-principles electronic structure calculations identify that the NLO responses arise from the presence ...

Crystal Growth and Associated Properties of a Nonlinear Optical Crystal—Ba2Zn(BO3)2

Crystals of Ba2Zn(BO3)2 were grown by the top-seeded solution growth (TSSG) method. The optimum flux system for growing Ba2Zn(BO3)2 crystals was 2BaF2:2.5B2O3. The transmission spectra of a (100)-orientated crystal indicated an absorption edge of 230 nm. Powder second-harmonic generation measurement revealed that Ba2Zn(BO3)2 can achieve type-I phase matching behavior at the fundamental wavelengths of 1064 and 532 nm respectively. The second-harmonic generating efficiency is around 0.85 and 0.58 times that of β-BaB2O4 when radiated with 1064 and 532 nm lasers.

A Cubic Non-Centrosymmetric Mixed-Valence Iron Borophosphate–Phosphite

A first member of a new family of metal borophosphate–phosphite Fe1.834IIFe0.166IIIB0.5[PO3(OH)]0.8(HPO3)2.033 has been successfully synthesized by using the boric acid–phosphorous acid flux. The compound crystallizes in the cubic crystal system in a non-centrosymmetric space group I4̅3d (No. 220) with unit cell parameters of a = 21.261(3) Å, and Z = 48, featuring a very condensed network of FeO6 octahedra and disordered phosphate-phosphite moieties with mixed valency of iron. The compound contains a novel fundamental building unit (FBU), a cyclic borophosphate-phosphite ring which is further connected to form a propeller like partial anionic structure. Metal polyhedra also form a propeller-like structure through edge-sharing and are further connected to the partial anionic structure to form the three-dimensional structure. Thermal analyses, infrared and Mössbauer spectroscopy, magnetic and second harmonic generating (SHG) measurements using 1064 nm radiation have been performed on this compound. SHG measurements indicate that the compound has an efficiency approximately equal to α-SiO2.

Growth and characterization of l-alanine admixtured urea single crystal

Single crystals of urea with l-alanine were grown by low temperature solution growth method from aqueous solution. The cell parameters and crystalline nature of the grown crystals were determined from single and powder X-ray diffraction studies. The qualitative analyses of the presence of functional groups in the grown crystals were estimated from FTIR analysis. The UV–visible spectrum reveals the optical property of the grown crystal. The second harmonic generating (SHG) properties are demonstrated using Kurtz–Perry powder technique. Photoluminescence shows that the grown crystal has a blue fluorescence emission. Photoconductivity study reveals the negative photoconductivity nature of the crystal. The low value of dielectric loss with high frequency for these samples suggests that the samples possess enhanced optical quality with lesser defects and this parameter is of vital importance.

Linear and nonlinear optical properties of unidirectionally grown L-Threonine acetate single crystals

Unidirectional <1 1 0> L-Threonine acetate (LTA) single crystal was grown and reported. The grown crystal was characterized by powder X-ray diffraction (XRD) studies to confirm the crystal structure. The optical band gap (Eg) value of the grown crystal is obtained from the tauc's plot of (αhv)2 vs hv which was determined by extrapolating the linear region of the curve to the hv axis where (αhv)2 = 0. Other linear optical parameters such as Extinction coefficient, Reflectance, Refractive index, Complex dielectric constant, and Optical conductivity are calculated for the grown crystal and its variation with incident photon energy is analysed. Second Harmonic Generating (SHG) efficiency of the candidate material was determined by Nd:YAG Q-switched laser Kurtz powder technique.

Pb4V6O16(SeO3)3(H2O), Pb2VO2(SeO3)2Cl, and PbVO2(SeO3)F: new lead(II)-vanadium(V) mixed-metal selenites featuring novel anionic skeletons.

Hydrothermal reactions of PbCO3 (or PbCl2), V2O5, and SeO2 in KOH solution or HF solution resulted in three new lead(II)-vanadium(V) mixed-metal selenites, namely, Pb4V6O16(SeO3)3(H2O) (1), Pb2VO2(SeO3)2Cl (2), and PbVO2(SeO3)F (3). Compounds 1 and 2 are polar (space group P21), whereas compound 3 is centrosymmetric (space group Pbca). Compound 1 displays an unusual [V6O16(SeO3)3](8-) anionic chain, which is composed by a 1D [V4O12](2-) anionic chain that is further decorated by dimeric [V2O6(SeO3)3](8-) units via corner-sharing. Compound 2 features two types of 1D chains, a cationic [Pb2Cl](3+) chain and a [VO2(SeO3)2](3-) anionic chain, whereas compound 3 contains dimeric [V2O4(SeO3)2F2](2-) units. The powder second-harmonic-generating (SHG) measurements indicate that compound 1 shows a weak SHG response of about 0.2 × KDP (KH2PO4) under 1400 nm laser radiation. Thermal stability and optical properties as well as theoretical calculations based on density functional theory methods were also performed.

Role of acentric displacements on the crystal structure and second-harmonic generating properties of RbPbCO3F and CsPbCO3F.

Two lead fluorocarbonates, RbPbCO3F and CsPbCO3F, were synthesized and characterized. The materials were synthesized through solvothermal and conventional solid-state techniques. RbPbCO3F and CsPbCO3F were structurally characterized by single-crystal X-ray diffraction and exhibit three-dimensional (3D) crystal structures consisting of corner-shared PbO6F2 polyhedra. For RbPbCO3F, infrared and ultraviolet–visible spectroscopy and thermogravimetric and differential thermal analysis measurements were performed. RbPbCO3F is a new noncentrosymmetric material and crystallizes in the achiral and nonpolar space group P6̅m2 (crystal class 6̅m2). Powder second-harmonic generation (SHG) measurements on RbPbCO3F and CsPbCO3F using 1064 nm radiation revealed an SHG efficiency of approximately 250 and 300 × α-SiO2, respectively. Charge constants d33 of approximately 72 and 94 pm/V were obtained for RbPbCO3F and CsPbCO3F, respectively, through converse piezoelectric measurements. Electronic structure calculations indicate that the nonlinear optical response originates from the distorted PbO6F2 polyhedra, because of the even–odd parity mixing of the O 2p states with the nearly spherically symmetric 6s electrons of Pb2+. The degree of inversion symmetry breaking is quantified using a mode-polarization vector analysis and is correlated with cation size mismatch, from which it is possible to deduce the acentric properties of 3D alkali-metal fluorocarbonates.

Coating barium titanate nanoparticles with polyethylenimine improves cellular uptake and allows for coupled imaging and gene delivery

Barium titanate nanoparticles (BT NP) belong to a class of second harmonic generating (SHG) nanoprobes that have recently demonstrated promise in biological imaging. Unfortunately, BT NPs display low cellular uptake efficiencies, which may be a problem if cellular internalization is desired or required for a particular application. To overcome this issue, while concomitantly developing a particle platform that can also deliver nucleic acids into cells, we coated the BT NPs with the cationic polymer polyethylenimine (PEI)–one of the most effective nonviral gene delivery agents. Coating of BT with PEI yielded complexes with positive zeta potentials and resulted in an 8-fold increase in cellular uptake of the BT NPs. Importantly, we were able to achieve high levels of gene delivery with the BT-PEI/DNA complexes, supporting further efforts to generate BT platforms for coupled imaging and gene therapy.

Large scale synthesis, second-harmonic generation, and piezoelectric properties of a noncentrosymmetric vanadium phosphate, Li2VPO6

The phase pure large scale synthesis, second-harmonic generation, and piezoelectric properties of a vanadium phosphate, Li2VPO6 are reported. The material has been synthesized by a standard solid-state reaction using Li2CO3, V2O5, and NH4H2PO4 as reagents. The phase purity and crystal structure of the reported material have been confirmed by powder X-ray and neutron diffractions. The material crystallizes in orthorhombic space group Pna21 (no. 33) with a=10.32581(7) Å, b=4.63728(3) Å, c=8.56606(5) Å, and Z=4. The noncentrosymmetric layered structure is composed of distorted VO6 octahedra and PO4 tetrahedra. The V5+ cations distort either along the approximate [1 0 1] or [−1 0 1] directions attributable to the alignment of distorted VO6 octahedra, resulting in a polar structure. Powder second-harmonic generating (SHG) measurements on Li2VPO6 using 1064 nm radiation, indicate the material has a SHG efficiency of approximately 10 times that of α-SiO2 and is not phase-matchable (type 1). Converse piezoelectric measurements for the material reveal a piezoelectric coefficient, d33, of 12 pm V−1.

Linear and Nonlinear Optical Properties of L- Histidinium Perchlorate (LHPCl) Single Crystal

L- Histidinium Perchlorate, a semi organic nonlinear optical material was grown by solution growth method. The absorption studies show minimum absorption in the entire visible region. The optical band gap (Eg) value of the grown crystal is obtained from the tauc’s plot of (αhν)2 vs hν which was determined by extrapolating the linear region of the curve to the hν axis where (αhν)2=0. Furthermore linear optical parameters such as Extinction coefficient, Reflectance, Refractive index, Complex dielectric constant and Optical conductivity are calculated and its variation with incident photon energy is analyzed. Second Harmonic Generating (SHG) efficiency of the candidate material was determined by Nd:YAG Q-switched laser Kurtz powder techinqe and its 3.19 times greater than KDP.

Surface functionalization of barium titanate SHG nanoprobes for in vivo imaging in zebrafish

To address the need for a bright, photostable labeling tool that allows long-term in vivo imaging in whole organisms, we recently introduced second harmonic generating (SHG) nanoprobes. Here we present a protocol for the preparation and use of a particular SHG nanoprobe label, barium titanate (BT), for in vivo imaging in living zebrafish embryos. Chemical treatment of the BT nanoparticles results in surface coating with amine-terminal groups, which act as a platform for a variety of chemical modifications for biological applications. Here we describe cross-linking of BT to a biotin-linked moiety using click chemistry methods and coating of BT with nonreactive poly(ethylene glycol) (PEG). We also provide details for injecting PEG-coated SHG nanoprobes into zygote-stage zebrafish embryos, and in vivo imaging of SHG nanoprobes during gastrulation and segmentation. Implementing the PROCEDURE requires a basic understanding of laser-scanning microscopy, experience with handling zebrafish embryos and chemistry laboratory experience. Functionalization of the SHG nanoprobes takes ∼3 d, whereas zebrafish preparation, injection and imaging setup should take approximately 2-4 h.

Solvothermal synthesis, crystal structure, and second-order nonlinear optical properties of a new noncentrosymmetric gallium-organic framework material, [N(C3H7)4]3Ga3[C6H3(CO2)3

A novel noncentrosymmetric (NCS) gallium-organic framework material, [N(C3H7)4]3Ga3[C6H3(CO2)3]4 (CAUMOF-11) has been synthesized by a solvothermal reaction using Ga(NO3)3·xH2O, 1,3,5-C6H3(CO2H)3, N(C3H7)4Cl, HNO3, and HCON(CH3)2 at 180°C. The structure of the reported material has been determined by single-crystal X-ray diffraction. CAUMOF-11 has an anionic three-dimensional framework with aligned four-coordinate GaO4 tetrahedra and 1,3,5-benzenetricarboxylate groups. Tetrapropylammonim cations reside within the channel and maintain the charge balance. Detailed structural analyses with full characterization including infrared spectroscopy, thermogravimetric analysis, elemental analysis, ion-exchange reactions, topotactic decomposition, and gas adsorption experiments are reported. Powder second-harmonic generating (SHG) measurements on CAUMOF-11, using 1064nm radiation, exhibit SHG efficiency of 15 times that of α-SiO2 and the material is phase-matchable (type-1).

Influence of the Cation Size on the Framework Structures and Space Group Centricities in AMo2O5(SeO3)2 (A = Sr, Pb, and Ba)

Two new quaternary mixed-metal selenites, SrMo(2)O(5)(SeO(3))(2) and PbMo(2)O(5)(SeO(3))(2), have been synthesized as crystals and pure polycrystalline phases by standard solid-state reactions using SrMoO(4), PbO, MoO(3), and SeO(2) as reagents. The crystal structures of the reported materials have been determined by single-crystal X-ray diffraction. SrMo(2)O(5)(SeO(3))(2) and PbMo(2)O(5)(SeO(3))(2) are isostructural and crystallized in the triclinic centrosymmetric space group P1̅ (No. 2). The reported materials exhibit chain structures consisting of MoO(6) octahedra and asymmetric SeO(3) polyhedra. Complete characterizations including IR spectroscopy and thermal analyses for the compounds are also presented, as are dipole moment calculations. In addition, the powder second-harmonic-generating (SHG) properties of noncentrosymmetric polar BaMo(2)O(5)(SeO(3))(2) have been measured using 1064 nm radiation. Through powder SHG measurement, we are able to determine that BaMo(2)O(5)(SeO(3))(2) has a SHG efficiency of approximately 80 times that of α-SiO(2). Additional SHG measurements reveal that the material is phase-matchable (type 1). A detailed cation size effect on the symmetry and framework structure is discussed.

SHG nanoprobes: Advancing harmonic imaging in biology

Second harmonic generating (SHG) nanoprobes have recently emerged as versatile and durable labels suitable for in vivo imaging, circumventing many of the inherent drawbacks encountered with classical fluorescent probes. Since their nanocrystalline structure lacks a central point of symmetry, they are capable of generating second harmonic signal under intense illumination - converting two photons into one photon of half the incident wavelength - and can be detected by conventional two-photon microscopy. Because the optical signal of SHG nanoprobes is based on scattering, rather than absorption as in the case of fluorescent probes, they neither bleach nor blink, and the signal does not saturate with increasing illumination intensity. When SHG nanoprobes are used to image live tissue, the SHG signal can be detected with little background signal, and they are physiologically inert, showing excellent long-term photostability. Because of their photophysical properties, SHG nanoprobes provide unique advantages for molecular imaging of living cells and tissues with unmatched sensitivity and temporal resolution.

ZnIO3(OH): a new layered noncentrosymmetric polar iodate – hydrothermal synthesis, crystal structure, and second-harmonic generating (SHG) properties

A new noncentrosymmetric polar iodate material, ZnIO(3)(OH), has been hydrothermally synthesized as crystals and pure powders by using ZnO (or Zn(CH(3)CO(2))(2)·2H(2)O), HIO(3), and water. Single crystal X-ray diffraction was used to determine the crystal structure of the reported material. ZnIO(3)(OH) exhibits a layered structure that is composed of ZnO(6) and IO(3) polyhedra. Powder nonlinear optical (NLO) properties measurements on ZnIO(3)(OH) using 1064 nm radiation indicate the material has a second-harmonic generating (SHG) efficiency of approximately 20 times that of α-SiO(2). Additional SHG measurements reveal that the material is not phase-matchable (type 1). Infrared spectroscopy, elemental analysis, and thermogravimetric analysis for the reported compound are also presented. Crystal data: ZnIO(3)(OH), monoclinic, space group Cc (no. 9) with a = 4.67670(10) Å, b = 11.2392(4) Å, c = 6.3308(2) Å, β = 90.019(2)°, and Z = 4.

Second-harmonic generating properties of polar noncentrosymmetric aluminoborate solid solutions, Al5−xGaxBO9 (0.0 ≤x≤ 0.5)

A series of solid solutions of polar aluminoborate materials, Al(5-x)Ga(x)BO(9) (0.0 ≤x≤ 0.5) have been synthesized by standard solid-state reactions using Al(2)O(3), Ga(2)O(5), and B(OH)(3) as reagents. The phase purities, crystal structures, and solid solution behavior of the reported materials have been investigated by powder X-ray diffraction. Solid solutions of Al(5-x)Ga(x)BO(9) crystallize in the polar noncentrosymmetric space group, Cmc2(1), with a three-dimensional structure consisting of distorted MO(4), MO(5), MO(6), and BO(3) polyhedra (M = Al or Ga). Powder second-harmonic generating (SHG) measurements on the Al(5)BO(9) using 1064 nm radiation, indicate the material has a SHG efficiency of approximately 2 times that of α-SiO(2) and is not phase-matchable (type 1). Further nonlinear optical (NLO) measurements on the Al(5-x)Ga(x)BO(9) solid solutions indicate a sharp increase in SHG efficiency up to 10 times that of α-SiO(2) for x≥ 0.4. Close structural examination suggests that the alignment of the asymmetric π-delocalization of BO(3) groups is responsible for the abrupt increase of SHG efficiency.

Synthesis, growth, and characterization of a new NLO material 3-(2,3-dimethoxyphenyl)-1-(pyridin-2-yl)prop-2-en-1-one

3-(2,3-Dimethoxyphenyl)-1-(pyridin-2-yl)prop-2-en-1-one (DMPP) a potential second harmonic generating (SHG) has been synthesized and grown as a single crystal by the slow evaporation technique at ambient temperature. The structure determination of the grown crystal was done by single crystal X-ray diffraction study. DMPP crystallizes with orthorhombic system with cell parameters a = 20.3106(8)angstrom, b = 4.9574(2)angstrom, c = 13.4863(5)angstrom, alpha = 90 degrees, beta = 90 degrees, gamma = 90 degrees and space group Pca2(1). The crystals were characterized by FT-IR, thermal analysis, UV-vis-NIR spectroscopy and SHG measurements. Various functional groups present in DMPP were ascertained by FTIR analysis. DMPP is thermally stable up to 80 degrees C and optically transparent in the visible region. The crystal exhibits SHG efficiency comparable to that of KDP. (C) 2011 Elsevier B.V. All rights reserved.